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Title: Finite Element Analysis and design of Ferrite Phase Shifters
Author: Zafar, Junaid
ISNI:       0000 0004 2676 0235
Awarding Body: The University of Manchester
Current Institution: University of Manchester
Date of Award: 2009
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Signal routing at Watts and KiloWatts is primarily handled by using waveguides or stripline structures containing magnetized ferrites. Over the last. 50 years, many ferrite phase shift and control devices have been developed across the microwave spectrum for a wide range of power levels and now commercially available. However, many challenges remain to be addressed if this body of knowledge is to be extended to meet demands for miniaturization, broader relative bandwidths, and higher operating frequencies at reduced costs. Ferrite technology still remains to a great extent "a black art" because the design of ferrite phase shift and control devices is primarily based on the empirical approximations, circuit models and extensive experimentation. In this work a non-Hermitian gyro tropic finite element formulation is presented for the modelling of gyromagnetic structures. The tensor permeability expressions which are incumbent for the proper characterization of gyromagnetic components have been derived and used in the derivation of a generic finite element (FE) functional for gyromagnetic components. The functional is developed from Maxwell's coupled equations before demonstrating its stationary properties at the boundary value problem solution. The formulation is implemented with finite element method to ensure that only physical eigen solutions exist. This four-transverse field functional formulation evaluates complex propagation constant as its eigen value. The method is then applied to design a twin toroidal ferrite phase shifter with a low reluctance magnetic bias circuit. Viscous plastic processing method (VPP) is used to fabricate ferrite toroids to ensure a homogeneous grain structure with continuous shape. VPP fabrication technique confers improved ferrite properties with reduce low-field loss and threshold for spinwave instability; this is imperative in high quality, partially magnetized devices. A closed form field formulation is used to design matching quarter wavelength impedance transformers by calculating the fields and dispersion expressions for the matching section. This compact and power efficient devi~e was then tested. The insertion loss was less than IdB over the frequency band from 9.5-10.3GHz and return loss of 20dB was achievable. The phase shift calculations agree to within 10% of the measured values. The variational finite element formulation developed in chapter 5, is further used to design and fabricate a high power partial height ferrite phase shifter. At high power levels nonlinear loss is prevalent but this has been avoided using a technique called "mode segregation" by biasing the ferrite above ferrimagnetic resonance. The above. resonance operation requires larger external bias fields. The calculations agree well with the experimental data.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available